Objective To assess the relationship between of androgen deprivation therapy (ADT) and the mood of prostate cancer (PCa) patients and partners of PCa patients. Methods PCa patients (n = 295) and partners of patients (n = 84) completed an online survey assessing the patients' current mood and mood prior to treatment, relationship adjustment, and sexual function. We compared men on ADT to men who received non‐hormonal treatments for their PCa. Results Patients currently treated with ADT (n = 82) reported worsened mood as measured by the Profile of Mood States compared to those not on ADT (n = 213). The negative impact of ADT on mood, however, was reduced in older patients. Partners of patients on ADT (n = 42) reported similar declines in the patient's mood that patients reported, but to a greater degree than patient‐reported levels. Conclusions Our data support ADT's impact on PCa patients' mood and verify that partners concurrently see the effects. The psychological changes related to ADT can impact relationships and affect the quality of life of both PCa patients and partners. Patients and their partners are likely to benefit from being well informed about the psychological effects of androgen deprivation on men beginning ADT. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.